In a manufacturing process of a semiconductor device, a FPD (flat panel display), an organic EL (Electro Luminescence) element, a solar cell and the like, a semiconductor substrate, a glass substrate or the like is subjected to various processes such as film forming, etching, ashing, oxidation, nitriding, doping, diffusion and the like. These processes are performed in depressurized processing chambers if plasma is used.
A multi-chamber type substrate processing system for performing simultaneous substrate processing in a plurality of processing chambers is commonly used to improve a throughput. FIG. 1 shows a substrate processing system as an example of conventional multi-chamber type substrate processing systems in which sets of a processing chamber 1 and a load-lock chamber 2 in one-to-one correspondence are connected to a loader module 3 (see, e.g., Japanese Patent Application Publication No. JP 2002-151568). A plurality of cassette ports 4 is provided with the loader module 3. An atmospheric transfer robot 5 in the loader module 3 transfers substrates in the cassettes 6 into the load-lock chambers 2. The interior of each load-lock chamber 2 alternates between a vacuum condition and an atmospheric condition. A vacuum transfer robot 7 to transfer a substrate, which has been transferred into the load-lock chamber 2, into a corresponding processing chamber 1 is provided in the load-lock chamber 2. When the atmospheric transfer robot 7 transfers the substrate into the load-lock chamber 2, the interior of the load-lock chamber 2 goes into the atmospheric condition. When the vacuum transfer robot 7 transfers the substrate into the processing chamber 1, the interior of the load-lock chamber goes into the vacuum condition.
The substrate processing system shown in FIG. 1 has a merit in that substrate processing can be carried out without interruption by one vacuum transfer robot 7 even in a case where the other is out of order. However, the substrate processing system has a drawback in that the substrate cannot be continuously processed under vacuum condition when the substrate has to be moved between the processing chambers 1 because the substrate needs to pass through the atmosphere of the loader module 3 before it is passed over from one processing chamber 1 to another.
In order to overcome the drawback of the above substrate processing system, there has been proposed a cluster type substrate processing system as shown in FIG. 2. As shown, a transfer chamber 10 provided with a vacuum transfer robot 9 is disposed in the center of this substrate processing system. A plurality of processing chambers 11 is arranged around the transfer chamber 10 in such a manner that they surround the transfer chamber 10. The transfer chamber 10 is connected to a loader module 13 via two load-lock chambers 12. The loader module 13 is provided with an atmospheric transfer robot 14. The atmospheric transfer robot 14 transfers a substrate in a cassette placed on each port 15 into the load-lock chamber 12. The vacuum transfer robot 9 in the transfer chamber 10 transfers the substrate, which has been transferred into the load-lock chamber 12, into the processing chamber 11.
The substrate processing system shown in FIG. 2 has a merit in that the substrates can be continuously processed in vacuum without being exposed to the atmosphere since the substrates pass through the transfer chamber 10 when the substrates are moved from one processing chamber 11 to another. However, since one vacuum transfer robot 9 has to cope with the plurality of processing chambers 11, if a time taken for a process performed in each processing chamber 11 is relatively short, a throughput (number of substrates processed per unit time) cannot be improved due to restriction on a transfer speed of the vacuum transfer robot 9. That is, if the process time of each processing chamber 11 is short, the transfer speed of the vacuum transfer robot 9 becomes a rate-determining factor and there occurs a delay time during which processed substrates wait within the processing chambers 11 without being unloaded. In other words, the transfer speed of the vacuum transfer robot 9 determines a process speed of the whole system. Moreover, as substrate size tends to be increased (e.g., from 300 mm to 450 mm in diameter for semiconductor wafers) in recent years, the whole substrate processing system including the processing chambers 11 is required to be extended. However, such simple extension of the substrate processing system may result in a bulky footprint.
For the purpose of reducing the footprint of the above-mentioned cluster type substrate processing system, Patent Document 3 discloses a multi-stage substrate processing system in which processing chambers 101 and 102 and load-lock chambers 2 are vertically stacked in a two-stage, respectively, and a vacuum transfer robot 42 provided in a central transfer chamber 3 is vertically moved so that the vacuum transfer robot 42 can transfer a substrate between the vertical two-stage load-lock chambers 2 and the vertical two-stage processing chambers 101 and 102.
In addition, for the purpose of reducing the footprint of the above-mentioned cluster type substrate processing system, Patent Document 4 discloses a multi-stage substrate processing system in which an elevatable robot arm 18 is placed in a central transfer chamber 30a, vertical multi-stage processing chambers 32a and vertical multi-stage load-lock chambers 34a are connected such that they surround the transfer chamber 30a, and the robot arm 18 transfers a substrate between the multi-stage processing chambers 32a and the multi-stage load-lock chambers 34a. In the substrate processing system of Patent Document 4, the respective multi-stage processing chambers 32a and the respective multi-stage load-lock chambers 34a can be vertically overlapped with each other either entirely or partially.
For the purpose of reducing the footprint of the substrate processing system, Patent Document 5 discloses a substrate processing system in which a rectangular transfer passage for transferring semiconductor wafers in an atmosphere is connected to a cassette stage 42 on which a plurality of cassettes 41 is loaded, vertical two-stage load-lock chambers 43 are connected to both sides of the rectangular transfer passage, and vertical two-stage processing chambers 45 are connected to the respective vertical two-stage load-lock chambers. In the rectangular transfer passage, there is provided with a transfer device 52 which receives the semiconductor wafer from the cassette and transfers the semiconductor wafer to the load-lock chamber 43.
Each load-lock chamber 43 is provided with a vacuum transfer device which receives the semiconductor wafer from the transfer device 52 and transfers the semiconductor wafer to the processing chamber 45. The interior of the load-lock chamber 43 alternates between a vacuum condition and an atmospheric condition. When the atmospheric transfer device 52 transfers the semiconductor wafer to the vacuum transfer device of the load-lock chamber 43, the interior of the load-lock chamber 43 turns into an atmospheric condition. On the other hand, when the vacuum transfer device of the load-lock chamber 43 transfers the semiconductor wafer to the processing chamber 45, the interior of the load-lock chamber 43 turns into a vacuum condition.